Malaria Control With Insecticide For Older Mosquitoes

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Certain entomologists have found that killing older mosquitoes with either chemical or biological insecticide may prove to be a more sustainable way of controlling malaria.

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Andrew Read, a Penn State professor of biology and entomology, says that the new approach to attack older mosquitoes may lead to evolution-proof insecticides that never become obsolete.

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He points out that most of the chemicals used to kill mosquitoes become ineffective because repeated exposure to an insecticide breeds a new generation of mosquitoes that are resistant to that particular insecticide.

"Insecticides sprayed on house walls or bed nets are some of the most successful ways of controlling malaria. But they work by killing the insects or denying them the human blood they turn into eggs. This imposes an enormous selection in favour of insecticide-resistant mosquitoes," he said.

He added: "If we killed only older mosquitoes we could control malaria and solve the problem of resistant mosquitoes. This could be done by changing the way we use existing insecticides, even by simply diluting them."

It is easier to kill aging mosquitoes with insecticides like DDT, but new generation pesticides could do it too. And now, the researchers are working with a biopesticide that kills older mosquitoes.

"It is one of the great ironies of malaria. Most mosquitoes do not live long enough to transmit the disease. To stop malaria, we only need to kill the old mosquitoes," said Read.

He also said that since most mosquitoes would die before they became dangerous, late-acting insecticides will not have much impact on breeding, and, thus, there will be much less pressure for the mosquitoes to evolve resistance.

"This means that late-life insecticides will be useful for much, much longer -- maybe forever -- than conventional insecticides. Insects usually have to pay a price for resistance, and if only a few older mosquitoes gain the benefits, evolutionary economics can stop resistance from ever spreading," said Read.

They invented a mathematical model, and, after its analysis, found that insecticides killing only mosquitoes that had completed at least four cycles of egg production reduced the number of infectious bites by about 95 percent.

The researchers also found that resistance to late-acting insecticides spread much more slowly among mosquitoes as compared to conventional insecticides, and that, in many cases, it never spread at all.

Read said that the development of biological or chemical insecticides that were more effective against older, malaria-infected mosquitoes could save the millions dollars that would have to be spent to endlessly find new insecticides to replace ones that had become ineffective.

He added: "Insecticides that kill indiscriminately impose maximal selection for mosquitoes that render those insecticides useless. Late-life acting insecticides would avoid that fate. Done right, a one-off investment could create a single insecticide that would solve the problem of mosquito resistance forever."

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